All those 'not of works' scriptures are about not of the purification works where circumcision IS THE SIGN:
The scriptures in Romans:
Romans 2:25 Circumcision has value if you observe the law, but if you break the law, you have become as though you had not been circumcised.
Romans 2:27 The one who is not circumcised physically and yet obeys the law will condemn you who, even though you have the written code and circumcision, are a lawbreaker.
Romans 2:28 A person is not a Jew who is one only outwardly, nor is circumcision merely outward and physical.
Romans 2:29 No, a person is a Jew who is one inwardly; and circumcision is circumcision of the heart, by the Spirit, not by the written code. Such a person’s praise is not from other people, but from God.
Romans 3:1 [ God’s Faithfulness ] What advantage, then, is there in being a Jew, or what value is there in circumcision?
Romans 4:11 And he received circumcision as a sign, a seal of the righteousness that he had by faith while he was still uncircumcised. So then, he is the father of all who believe but have not been circumcised, in order that righteousness might be credited to them.
The works of circumcision is the 'not of by works' Paul was speaking about.
Nowhere anywhere do any scriptures say 'not of by repenting of sins'.
It is about about the purification works where circumcision is the sign.